The importance of the dynamic state of the lipids in a biological membrane to functional properties such as transport, surface recognition, and enzyme activity is well recognized. This has led to intense study, particularly by NMR methods. Despite this attention no consensus exists on a model for these motions. This research is designed to shed new light on these questions by exploiting the ability of NMR experiments which create multispin order to observe cross-correlation effects in spin relaxation. When studying a 13CH2 (i.e. AX2) spin system, four independent dipolar spectral densities (JCHCH, JCHCH., JHH'HH'' and JCHCH,) tracked by traditional T1 relaxation experiments. Because these spectral densities have different sensitivities to motions of a given geometry, measurement of all four provides a stringent test of motional models. Myristic acids (MA's) will be synthesized which have been 13C labelled in the 2, 6, and 12 positions. These fatty acids will be incorporated into dimyristoylphosphatidylcholines (DMPC's). For NMR studies the free fatty acids will be prepared as micellar solutions of the sodium salts and the DMPC's will be prepared as micellar solutions of the sodium salts and the DMPC's will be prepared sonicated unilamellar vesicles. NMR studies of these systems will be carried out at field strengths ranging from 2.3 T (100 MHz 1H) to 11.7 T (500 MHz 1H). NMR studies of the labelled 13CH2 spin systems will include: (1) Coupled spin relaxation experiments, which follow the time evolution of the 13C triplet (in the absence of decoupling) after a variety of initial perturbations. Cross-correlation effects lead to differing rates of relaxation by the various 13C transitions. (2) Differential line broadening. Cross-correlation effects lead to the inner and two outer lines of the 13C triplet having different line widths. (3) Multiple quantum relaxation. Triple quantum filtered NOESY experiments show "forbidden" cross peaks, arising from cross-correlation effects.